E-mail virus protection system and method

ABSTRACT

A network is protected from e-mail viruses through the use of a sacrificial server. Any executable programs or other suspicious parts of incoming e-mail messages are forwarded to a sacrificial server, where they are converted to non-executable format such as Adobe Acrobat PDF and sent to the recipient. The sacrificial server is then checked for virus activity. After the execution is completed, the sacrificial server is rebooted.

REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 09/704,790, filed Nov. 3, 2000, now U.S. Pat. No. 6,901,519,which claims the benefit of U.S. Provisional Application No. 60/213,254,filed Jun. 22, 2000. The disclosures of both of those applications arehereby incorporated by reference in their entireties into the presentdisclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to computer systems and computernetworks. In particular, the present invention relates to a system andmethod for detecting and nullifying the effects of computer viruses.Still more particularly, the present invention relates to a system andmethod for detecting and nullifying the effects of computer viruses frommessages and attachments delivered by electronic mail through a network.

2. Description of the Related Art

Computer viruses are a destructive aspect of the computer revolutionthat threatens its potential growth and usability. Significant time andmoney are lost annually combating the effects of this insidious, andseemingly endemic, problem. A computer virus is actually just anunauthorized block of executable computer code purporting to be harmlessor is hidden in another valid computer program. Once the valid programis executed, the unauthorized virus code is also activated. The effectof such viruses can be simple pranks, such as causing messages to bedisplayed on the screen, or more serious activities, such as destroyingprograms and data. Once executed, they often spread quickly by attachingthemselves to other programs in the system. Infected programs may inturn continue the cancerous replication by copying the virus code tostill other programs. The proliferation of Internet E-mail has onlyaccelerated the problem in that local viruses can now spreadinternationally in a matter of hours.

Prior art attempts to reduce the effects of viruses and prevent theirproliferation by using various virus detection schemes have been onlymarginally successful. The reason for the limited success is that theprior art methods attempt to identify the existence of a virus beforetaking steps to protect a user. For example, many virus detectionprograms use a method known as “behavior interception,” which monitorsthe computer or system for key system functions such as “write,”“erase,” “format disk,” etc. When such operations occur, the virusdetection program prompts the user for input as to whether such anoperation is expected. If the suspect operation was not expected (e.g.,the user was not operating any program that employed such a function),the user can abort the operation. Another virus detection method, knownas “signature scanning,” scans program code that is being copied ontothe system. Again, the virus detector searches for recognizable patternsof program code, such as the program attempting to write into specificfile or memory locations, that betray the possible existence of a virus.Yet another prior art approach to virus detection performs a checksum(mathematical signature) on critical programs stored on a system thatare known to be free of viruses. If a virus later attaches itself to oneof these programs, the checksum value—which is periodicallyrecalculated—will be different and thus, the presence of a virusdetected.

While all of these methods work to some degree, they tend to suffer fromone critical drawback: They depend on recognizing the virus as a virusbefore instituting any protection for the user. All too often, new(unrecognized) viruses must first wreak havoc on a significant number ofvictims before the new virus' identifying characteristics are recognizedand included in the (ever-lengthening) watch lists of the various virusprotection programs available to government and industry.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byimplementing a system and method that eliminates the threat of virusestransmitted on a computer network by rendering any viruses inoperable.As discussed above, all viruses are programs. Like all programs, theyare designed to run in a specific or predictable environment. Virusesdepend on a host computer's operating system to recognize them as validprograms. They also depend on the host computer's central processingunit (CPU) to understand the virus' commands and obey them. Nonexecutable entities are, by nature, incapable of launching a virus.Therefore, if a host computer converts all data received via e-mail(mail and attachments) to non-executable entities, any embedded virus isrendered inoperable. The present invention describes a method and systemof virus protection that involves passing all e-mail and attachmentsthrough various conversion states that, while harmless to e-mail textand attachments, the conversions are lethal to executable code(viruses).

Even though the majority of e-mail received by a company or governmentagency should contain no valid executable components, a small percentageof e-mail attachments, such as “working drafts,” and standard contracttemplates may require user updating or valid executable macros.Therefore, the present invention also describes a system and method ofidentifying “Approved” embedded macros and—as long as they have not beenmodified—allowing them to survive the virus killing conversions.

Finally, the present invention also includes a unique “sacrificial PC”system and method capable of safely executing, detecting (viaexamination of the results of execution), and safely recovering frompotentially virus-laden e-mails.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment will be set forth in detail with reference to thedrawings, in which:

FIG. 1 shows a block diagram of an e-mail gatekeeper system;

FIGS. 2 and 2A show a flow chart of operations carried out in the e-mailgatekeeper system; and

FIG. 3 shows a flow chart of operations carried out by a sacrificialprocessor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Though not essential to every embodiment of this invention, thepreferred embodiment makes use of the following concepts and principles:

-   -   1. Recipients of e-mails are ultimately more qualified to        determine what information is acceptable than a generalized        software program or system    -   2. If given an opportunity, a user can clearly define which        e-mail types and attachments he or she does or does not wish to        receive.    -   3. The ability of users to accept macros and other forms of        executable code commonly used in modern computer generated        business forms and templates must be maintained.    -   4. All information is potentially important to a user.        Therefore, software systems, including security programs, should        not arbitrarily delete or withhold e-mail content without        specific knowledge and authorization of the owner of the e-mail        system.    -   5. The value of information tends to decrease over time.        Therefore, information contained in e-mails should not be        unreasonably delayed.

The gatekeeper method and system described herein operate under thefollowing rules and definitions:

-   1. Any macro or executable code that alters the physical appearance    of an e-mail or attachment is considered by the gatekeeper to be a    customized form.-   2. All customized forms requiring user input must be authorized by    the owner of the e-mail system.

In an effort to provide recipients with all of the contents of alle-mails and attachments (not prohibited by the owner of the e-mailsystem) all unauthorized form will be executed; however, the form'soutput (not the form itself) will be delivered to the user in a “safe”non-executable format.

The Gatekeeper method and system described defines and ability toauthorize and authenticate all forms.

The virus detection system and method of the present inventionpreferably operates on a system as depicted in FIG. 1.

An intermediary E-mail security server (102), referred to as “theGatekeeper” intercepts all e-mail messages and attachments sent by asender (101) via a communications network, such as the Internet (109).The arriving unopened e-mail and attachments are archived and logged(202) with a date and time stamp, plus any routing informationavailable. Address data is then stripped off of the e-mail (204) forattachment to the “safe” e-mail constructed at (210). The e-mail portionof the Internet e-mail received from (201) is passed through aconversion process (205) that eliminates all executable code leavingonly alphanumeric message text. Any imbedded hyperlinks or emailaddresses, while still identifiable as links or addresses, are renderedinoperable as executable “links.” The Gatekeeper (102) then checks tosee if the arriving e-mail contains an attachment (206). If the e-mailcontains no attachment, processing continues at step (210).

If the e-mail contains an attachment, the attachment types (extensions)are validated against several lists provided by the client during theinstallation process. The e-mail attachment type is first checkedagainst a list of client approved acceptable file extensions. If theattachment extension is not in the approved list, it is consideredeither disapproved or unknown. (212). If the attachment extension typeis found in the disapproved list, a message is constructed indicatingthat “this e-mail contains a disapproved attachment.” The disapprovalmessage is included in the safe e-mail constructed in step (210).

If the e-mail contains an attachment with an extension that is not ineither the “disapproved” or “approved” lists, the entire attachment ispassed through a conversion process (205) that eliminates all executablecode leaving only alphanumeric message text. This process will generallycreate a readable copy of the attachment, but will not allow theattachment to open any processes or applications, including executablevirus code. If the included attachment from (206) is of an approvedextension type, attachment inspection processing continues at (208),which checks the approved attachment extension to see if it contains anyexecutable code (macros). This process involves reading the attachmentfile's internal format and identifying any executable code, such asmacros that may be present. Any executable code found is noted andidentified for authentication (209). An encrypted authenticationidentifier is created for the executable code by passing it through analgorithm such as, a checksum or hashing algorithm (213), that uniquelyidentifies the string of executable code. The unique identifier is thenencrypted using a key known only to the Gatekeeper program or server.The authentication identifier is then compared to a list of approvedcode contained by the Gatekeeper and supplied by the Client (216). Sincethis system and method described validates only the executable code(macros), the non-executable data portion of the attachment can safelybe changed or updated interactively. If the attachment contains approvedmacros, the original attachment is made available to the recipient. Ifthe attachments contain unapproved macros, the attachment is forwardedto an available sacrificial PC processor (103) via data link (108) forconversion to a non-executable format and further detailed virustesting. The method just described for detecting, authenticating, andapproving a macro can be used to authenticate and approve any form ofexecutable code embedded in an attachment or in the body of an e-mailmessage. Such code can include compiled programs, interpretive code,scripts, batch language, markup language code, or the like located inany part of the e-mail message, including the body and the attachments.

Sacrificial PC processing begins with the original e-mail attachmentbeing passed to an available sacrificial PC (105) via a data link (108)connecting the Gatekeeper server (102) with the sacrificial PC. Once thetransfer of the attachment is complete the data link (108) isintentionally broken. This eliminates the possibility of any unintendedcommunications back to the Gatekeeper. The original attachment is thenopened using standard Windows application processing supplied by theclient (303). The opened attachment is then passed through a process(304) which converts the attachment to a non-executable image format,such as Portable Document Format (PDF). Note there are many suitableimage formats. The process would choose one selected by the client. Thesafe image format version of the attachment is then encrypted in thesacrificial PC's unique authentication key assigned by the Gatekeeper atstartup. The data link (108) to the Gatekeeper is then re-established(306) and the encrypted non-executable attachment is returned to theGatekeeper (307).

All communications from a sacrificial PC to the Gatekeeper areinterrogated by the Gatekeeper's communications processor (220). Beforebeing accepted by the Gatekeeper as a valid message, the data must passa strict authentication test (219). The authentication process is asfollows.

At System startup (and periodically, if desired) the Gatekeeper createsa randomly generated set of authentication parameters to be used by eachsacrificial PC when communicating with the Gatekeeper. When asacrificial PC wants to communicate with the Gatekeeper it first sends ahandshake packet to the Gatekeeper identifying the specific PCrequesting communication. It also sends a short (unencrypted) clear-textportion of the data to be communicated encapsulated within the handshakepacket.

Once the Gatekeeper acknowledges the handshake, the sacrificial PC sendsthe full information packet to the Gatekeeper. A random amount of thepacket has been encrypted in the sacrificial PC's unique key. Thespecific amount of data encrypted by the sacrificial PC was determinedby one of the authentication parameters sent by the Gatekeeper atstartup. The Gatekeeper decrypts all data packets it receives based onthe assumed key of the specific sacrificial PC. In other words, “If youare who you say you are, you encrypted your data in the following way.”Once decrypted, the Gatekeeper compares the clear text portion of thedata received in the handshake packet with the decrypted data packet(219). If they match, the data is accepted; if they do not, the data isnot accepted. The authentication technique is based on known “challengeand response” authentication techniques.

Once the sacrificial PC has sent the read only “safe” attachment back tothe Gatekeeper, a special validation process examines the sacrificial PCto determine if any unexpected changes have occurred (308) and (309) onthe sacrificial PC. Unexpected changes could include the addition ordeletion of files, files that change name, extension, or contentunexpectedly, (including morphing of the tested attachment itself),attempted sensing of the date and time features of the sacrificial PC,etc.

Also, when the opportunity is available, as with attachments createdusing the Microsoft suite of office products, the sacrificial PCprocessor takes advantage of the “Enable Macros” “Disable Macros”feature. This built-in feature makes it possible to open a documentwithout allowing any embedded code (macros) to execute. Two copies ofthe same document can then be created, one created with macros executedand one created without macros executed. The two copies of the samedocument can then be examined to determine if executing the macro hadany effect on the information content of the document. By comparing thetwo documents, the sacrificial PC can determine whether or not the macrois relevant to the particular document being tested.

If execution of the macro was necessary to produce the informationcontained in the tested document, then the macro's contribution iscontained in the print image copy of the document produced by thesacrificial PC when it executed the document with macros enabled. Thisis the copy that is sent to the recipient.

Similarly, if testing the document with “macros disabled” has no impacton the content of the document, then the suspect macro is not necessary.It logically follows then, that the suspect macro is either irrelevantto the content the particular version of the document being tested or,it is a virus. In either case, the sacrificial PC has intercepted andnullified the suspect macro's impact on the recipient.

Any unexpected changes in the system trigger a virus alert. Standarduser security processes alert all authorized personnel (309). A special“ghosting” reload of the operating system then takes place. The processis as follows.

Each Sacrificial PC is configured with two hard drives. Each hard driveis configured with a single active partition and contains a safe copy ofthe operating system obtained from the read-only device (110). Thedesignated active partition—defined at start-up—is “toggled” between thetwo physical hard drives. This is done to increase the speed ofreloading and to maximize the availability of sacrificial PCs. Theunused drive—which is the one used to test the last attachment—isre-loaded, via ghosting software (310), with a fresh copy of theoperating system obtained from the read only CD ROM (110). Theconnection between the Gatekeeper (102) and the sacrificial PC (105) isthen re-established.

Once the sacrificial PC is re-ghosted, it is brought back on line andthe GateKeeper assigns it a new authentication Key and encryption lengthparameter.

Once the Gatekeeper sends data to a sacrificial PC, it notes the timethe data was sent. If no data is received back from a sacrificial PCwithin a specified period of time (typically two minutes), theGatekeeper assumes the sacrificial PC has become the victim of a virusand died. When this occurs, the Gatekeeper signals a virus alert andrequests human intervention to recover the dead sacrificial PC.

The method and system described above can also be implemented with thesacrificial PC implemented as a virtual machine or environment in theoperating system of another computer. This computer could be thegatekeeper, an e-mail server or any other computer.

The method and system described above also be implemented with thegatekeeper system implemented as part of another system, such as acomponent of an already existing e-mail server.

The gatekeeper system and method described uses the file and macroauthentication and encrypted client approval techniques described aboveto protect itself from both internal and external “hacking” attacks thatmay attempt to substitute, modify, destroy or otherwise nullifygatekeeper files and programs.

While a preferred embodiment has been set forth in detail above, thoseskilled in the art who have reviewed the present disclosure will readilyappreciate that other embodiments can be realized within the scope ofthe invention. For example, the use of certain hardware, operatingsystems, or the like should be construed as illustrative rather thanlimiting. Therefore, the present invention should be construed aslimited only by the appended claims.

1. A method for protecting a network from a virus contained in an e-mailmessage as executable code, the method comprising: receiving the e-mailmessage; converting the executable code from an executable format to anon-executable format by using an application-level process whichretains an appearance, human readability, and semantic content of thee-mail message; and forwarding the non-executable format to a recipientof the e-mail message.
 2. The method of claim 1, wherein the executablecode is contained in a body of the e-mail message.
 3. The method ofclaim 2, wherein the executable code comprises a hypertext link, andwherein the converting comprises deactivating the hypertext link.
 4. Themethod of claim 1, wherein the executable code is contained in anattachment in the e-mail message.
 5. The method of claim 4, wherein theconverting comprises: forwarding the attachment from a gatekeeper serverto a sacrificial server; and converting the attachment to thenon-executable format on the sacrificial server.
 6. The method of claim5, wherein the converting further comprises examining the sacrificialserver for virus activity.
 7. A method for protecting a network from avirus contained in an e-mail message as executable code, the methodcomprising: receiving the e-mail message in a gatekeeper server;converting the executable code from an executable format to anon-executable format; and forwarding the non-executable format to arecipient of the e-mail message, wherein the executable code iscontained in an attachment in the email message; wherein the convertingcomprises: forwarding the attachment from the gatekeeper server to asacrificial server; converting the attachment to the non-executableformat on the sacrificial server; examining the sacrificial server forvirus activity; and rebooting the sacrificial sever from a safe copy ofan operating system obtained from a read-only device.
 8. A method forprotecting a network from a virus contained in an e-mail message asexecutable code, the method comprising: receiving the e-mail message ina gatekeeper server; converting the executable code from an executableformat to a non-executable format; and forwarding the non-executableformat to a recipient of the e-mail message, wherein the executable codeis contained in an attachment in the email message; wherein theconverting comprises: forwarding the attachment from the gatekeeperserver to a sacrificial server; converting the attachment to thenon-executable format on the sacrificial server; examining thesacrificial server for virus activity; and wherein communicationsbetween the gatekeeper server and the sacrificial server areauthenticated using a challenge-and-response technique.
 9. The method ofclaim 4, wherein the converting comprises: maintaining a list ofapproved attachment types; determining whether the attachment is of atype which is in the list of approved attachment types; and if theattachment is not of a type which is in the list of approved attachmenttypes, informing the recipient that a message containing a non-approvedattachment has been received.
 10. The method of claim 1, wherein theconverting comprises: maintaining a list of approved executable code;determining whether the executable code is in the list of approvedexecutable code; and deactivating the executable code if the executablecode is not in the list of approved executable code.
 11. The method ofclaim 10, wherein: the list of approved executable code includesinformation for determining whether the approved executable code hasbeen altered; and the converting further comprises: determining whetherthe executable code has been altered; and deactivating the executablecode if the executable code has been altered.
 12. The method of claim11, wherein the determining whether the executable code has been alteredis performed through an algorithmic technique.
 13. The method of claim12, wherein the algorithmic technique is a check-summing technique. 14.The method of claim 12, wherein the algorithmic technique is a hashingtechnique.
 15. The method of claim 1, wherein the converting comprises:forming a first copy and a second copy of at least a portion of thee-mail message containing the executable code; executing the executablecode in the first copy but not the second copy; and after the executablecode in the first copy has been executed, comparing the first copy tothe second copy to determine an effect of the executable code.
 16. Asystem for protecting a network from a virus contained in an e-mailmessage as executable code, the system comprising: a workstationcomputer on the network used by a recipient of the e-mail message; and acomputer on the network for converting the executable code from anexecutable format to a non-executable format by using anapplication-level process which retains an appearance, human readabilityand semantic content of the e-mail message and forwarding thenon-executable format to the recipient.
 17. The system of claim 16,wherein the executable code is contained in a body of the e-mailmessage.
 18. The system of claim 17, wherein the executable codecomprises a hypertext link, and wherein the computer for convertingdeactivates the hypertext link.
 19. The system of claim 16, wherein theexecutable code is contained in an attachment in the e-mail message. 20.The system of claim 16, wherein the computer for converting is asacrificial server.
 21. The system of claim 20, wherein the sacrificialserver is examined for virus activity.
 22. A system for protecting anetwork from a virus contained in an e-mail message as executable code,the system comprising: a workstation computer on the network used by arecipient of the e-mail message; a gatekeeper server, in communicationwith the workstation computer over the network, for receiving the e-mailmessage; and a computer on the network for converting the executablecode from an executable format to a non-executable format and forwardingthe non-executable format to the workstation computer, wherein thecomputer for converting is a sacrificial server which is separate fromthe gatekeeper sever, wherein the sacrificial server is examined forvirus activity, wherein the network further comprises a read-onlydevice, and wherein the sacrificial server is rebooted from a safe copyof an operating system obtained from the read-only device.
 23. A systemfor protecting a network from a virus contained in an e-mail message asexecutable code, the system comprising: a workstation computer on thenetwork used by a recipient of the e-mail message; a gatekeeper server,in communication with the workstation computer over the network, forreceiving the e-mail message; and a computer on the network forconverting the executable code from an executable format to anon-executable format and forwarding the non-executable format to theworkstation computer, wherein the computer for converting is asacrificial server which is separate from the gatekeeper sever, whereinthe sacrificial server is examined for virus activity, whereincommunications between the gatekeeper server and the sacrificial serverare authenticated using a challenge-and-response technique.
 24. Thesystem of claim 16, wherein the network maintains a list of approvedattachment types, determines whether the attachment is of a type whichis in the list of approved attachment types, and, if the attachment isnot of a type which is in the list of approved attachment types, informsthe recipient that a message containing a non-approved attachment hasbeen received.
 25. The system of claim 16, wherein the network maintainsa list of approved executable code, determines whether the executablecode is in the list of approved executable code, and deactivates theexecutable code if the executable code is not in the list of approvedexecutable code.
 26. The system of claim 25, wherein: the list ofapproved executable code includes information for determining whetherthe approved executable code has been altered; the network determineswhether the executable code has been altered; and the executable code isdeactivated if the executable code has been altered.
 27. The system ofclaim 26, wherein the system determines whether the executable code hasbeen altered through an algorithmic technique.
 28. The system of claim27, wherein the algorithmic technique is a check-summing technique. 29.The system of claim 27, wherein the algorithmic technique is a hashingtechnique.
 30. The system of claim 16, wherein the computer forconverting converts the executable code by: forming a first copy and asecond copy of at least a portion of the e-mail message containing theexecutable code; executing the executable code in the first copy but notthe second copy; and after the executable code in the first copy hasbeen executed, comparing the first copy to the second copy to determinean effect of the executable code.
 31. A sacrificial server for use on anetwork, the sacrificial server comprising: communication means forreceiving an e-mail attachment from the network; and processing meansfor converting the e-mail attachment from an executable format to anon-executable format by using an application-level process whichretains an appearance, human readability and semantic content of thee-mail message and for returning the e-mail attachment to the network.32. The sacrificial server of claim 31, wherein the sacrificial serveris examined for virus activity.
 33. The sacrificial server of claim 32,wherein the sacrificial server further comprises a read-only device andis rebooted from a safe copy of an operating system obtained from theread-only device.
 34. The sacrificial server of claim 31, whereincommunications between the network and the sacrificial server areauthenticated using a challenge-and-response technique.
 35. Thesacrificial server of claim 31, wherein the sacrificial server stores alist of approved attachment types, determines whether the attachment isof a type which is in the list of approved attachment types, and, if theattachment is not of a type which is in the list of approved attachmenttypes, informs the network that a message containing a non-approvedattachment has been received.
 36. The sacrificial server of claim 31,wherein the sacrificial server maintains a list of approved executablecode, determines whether the attachment contains executable code andwhether the executable code is in the list of approved executable code,and deactivates the executable code if the executable code is not in thelist of approved executable code.
 37. The sacrificial server of claim36, wherein: the list of approved executable code includes informationfor determining whether the approved executable code has been altered;if the executable code is in the list of approved executable code, thesacrificial server determines whether the executable code has beenaltered; and the executable code is deactivated if the executable codehas been altered.
 38. The sacrificial server of claim 32, wherein thesacrificial server determines whether the executable code has beenaltered through the use of an algorithmic technique.
 39. The sacrificialserver of claim 38, wherein the algorithmic technique is a check-summingtechnique.
 40. The sacrificial server of claim 38, wherein thealgorithmic technique is a hashing technique.
 41. The sacrificial serverof claim 31, wherein the processing means converts the executable codeby: forming a first copy and a second copy of at least a portion of thee-mail message containing the executable code; executing the executablecode in the first copy but not the second copy; and after the executablecode in the first copy has been executed, comparing the first copy tothe second copy to determine an effect of the executable code.